1. Field of the Invention
The present invention relates to a Liquid Crystal Display (LCD) backlight inverter and, more particularly, to an LCD backlight inverter capable of a soft start that allows stable supply of initial current and voltage during initial driving of an LCD backlight lamp, thereby preventing over-current or over-voltage from being applied which would otherwise damage the LCD backlight lamp.
2. Description of the Related Art
In general, display devices for computer monitors, TVs and the like include those capable of generating light on their own such as Organic Light Emitting Displays (OLEDs), Vacuum Fluorescent Displays (VFDs), FieldEmission Displays (FEDs) and Plasma Display Panels (PDP), and those incapable of generating light on their own and requiring a separate light source such as Liquid Crystal Displays (LCDs).
A general LCD includes two panels each with field-generating electrodes and an anisotropic liquid crystal layer disposed between the panels. To obtain a desired image, a voltage is applied to the field-generating electrodes to generate an electric field in the liquid crystal layer and the voltage is varied to adjust the magnitude of this electric field, thereby adjusting the transmission ratio of the light passing through the liquid crystal layer.
At this time, the LCD can use natural light, but typically uses an artificial light source (backlight) separately prepared.
The backlight of the LCD can be categorized into an edge type (side-emitting type) and a direct type. In the edge-type backlight, a bar-type light source is located at a side of the LCD panel to irradiate light via a light guide panel to the LCD panel. In the direct type, a surface light source having an almost the same area as the LCD panel is disposed underneath the LCD panel to irradiate light directly to the surface of the LCD panel.
The LCD backlight adopts a fluorescent lamp or a light emitting diode as alight source. The fluorescent lamp includes Cold Cathode Fluorescent Lamp (CCFL), External Electrode Fluorescent Lamp (EEFL) and the like depending on the driving method. Such a fluorescent lamp generates electric discharge in response to power application to emit light. In order to maintain the electric discharge, the fluorescent lamp requires an alternate current. An inverter receives and converts a direct current into an alternative current, supplying the alternative current to the fluorescent lamp.
FIG. 1 is a circuit diagram illustrating an LCD backlight inverter for generating a Pulse Width Modulation (PWM) control signal according to the prior art.
As shown in FIG. 1, the conventional LCD backlight inverter includes an error detector 110 and a PWM comparator 120. The error detector 110 receives, by feedback, a feedback reference voltage indicating the size of current supplied to a lamp and compares the feedback voltage with a reference voltage to convert the difference into an error signal. A PWM comparator 120 compares the error signal with a triangle-wave oscillation signal to output a PWM signal with a predetermined duty ratio.
In the conventional LCD backlight inverter, the feedback reference voltage S11 and the reference voltage S12 are inputted to the error detector 110 and the difference between the two is amplified to generate the error signal S13. The error signal S13 is fed back to the error detector 110 via a capacitor 111.
Then, the error signal S13 is inputted to a PWM comparator 120, which compares the error signal S13 with a triangle-wave oscillation signal S14 separately inputted, thereby generating a PWM control signal S15.
The duty ratio of the PWM control signal S15 is determined by the error signal S13 of the error detector 110, and in accordance with the duty ratio, the current flowing to the fluorescent lamp (not shown) varies. The current of the fluorescent lamp is fed back to the error detector 110 as a feedback reference voltage S11 so as to regulate the current flowing to the lamp.
In the conventional LCD backlight inverter, however, the error signal S13 suddenly increases due to sudden increase of the PWM duty ratio during the initial driving. This results in application of over-voltage or over-current to the fluorescent lamp, damaging the fluorescent lamp.